Abbreviations:
3GPP3rd Generation Partnership ProjectHSDPAHigh Speed Downlink Packet AccessHS-TTIHigh Speed transport time intervalHS-DATAHigh Speed dataUEUser EquipmentRNCRadio Network Controller
The 3rd Generation Partnership Project (3GPP) specification is a standard for the third generation mobile telephony system. The system support uses different user data rates for different users. The transmission power used for a certain user is determined by interference level in a certain cell, user data rate, channel quality and requested quality of the data transmission in the cell.
HSDPA is a data transmission system that is a part of the 3GPP standard and is mainly used for best effort downlink transmission packet service, i.e. the transmission delay is not critical.
It is previously known that a base station (a.k.a. node B) operates the cell and that a scheduling algorithm situated in Node B decides to what user equipment (UE) data shall be transmitted. The UE may be any mobile or fixed equipment operated by a person on foot or in a vehicle. The decision from the scheduler is performed for every time slot. i.e. every Transport Time Interval (TTI). There is one base station and thus one scheduler for each cell in a system with a number of cells.
The scheduler can be based on several parameters e.g. data waiting time, channel quality, UE capabilities and priority of important data. Node B can transmit data to several UE in parallel within a TTI.
Problems with existing solutions are interference for a HSDPA channel to a specific UE. The interference mainly consist of thermal noise, transmitted power from other cells, dedicated channel power transmitted in the cell, power for common channels other than HSDPA in the cell, and transmitted HSDPA power to other UEs in the cell.
In order to maximize the data throughput, it is desired to minimise the interference that arises at the UE. It is previously known to do this by introducing beam forming functions (i.e. adaptive antenna system). The adaptive antenna system uses the beam forming function to cover only one or several cell segments in which cell segments are separated in space. This will reduce interference from other cells as well as from the actual cell since the antenna operates in one or several determined directions and therefore will not transmit in an omni-directional manner. The UE in a first cell segment will not be affected by the transmission in a second cell segment. Furthermore, the adjacent cell placed outside the beam forming direction will not be affected by the transmission. However, if there are a number of UEs in the same cell segment, the transmitted power to the different UEs will still interfere. For example, if user equipment UE1 and user equipment UE2 occupy the same cell segment and if Node B transmits data to both the UEs, then the both UEs will interfere each other.
For all channels except HSDPA channels the RNC decides when to transmit data. This means that interference cannot be avoided in node B in those cases where the UEs are in the same direction, i.e. in the same cell segment.
Hence, there still is a need for a better transmission of information in a cell comprising a number of user equipments such that the intracell interference is minimised when using a data transmission system, for example HSDPA.